Tumor cell growth can be controlled by surrounding normal cells. This process is called "heterologous growth control". The goal of this project is to elucidate mechanisms underlying this process. We will determine how nontransformed cells affect the Src signaling cascade in neighboring transformed cells. The need for heterologous gap junctional communication in heterologous growth control will be evaluated in Specific Aim 1. We hypothesize that nontransformed cells do not need to form active gap junction channels with Src transformed cells to normalize their growth. We will utilize connexin knockout cells, chemical blockers or antisense nucleic acids to suppress gap junctional communication. Intercellular communication will be examined by the transfer of fluorescent dyes, endogenous metabolites, and electrical conductance. If heterologous growth control occurs in the absence of gap junctional communication, then, as we hypothesize, gap junctional communication is not required for heterologous growth control. Effects of nontransformed cells on the Src kinase activity, and the activity of kinases acting downstream of Src, in Src transformed cells will be evaluated in Specific Aims 2 and 3, respectively. We hypothesize that nontransformed cells quell Src kinase activity, and affect the activity of downstream kinases, in neighboring transformed cells. We will use novel techniques that we have developed to examine kinase activity in transformed cells that are morphologically reversed to a normal phenotype by neighboring nontransformed cells. Our hypothesis will be proven if the Src signaling in transformed cells cascade is blocked by communication with nontransformed cells. Effects of nontransformed cells on the global expression pattern of genes in neighboring transformed cells will be examined in Specific Aim 4. We hypothesize that nontransformed cells alter the expression of specific genes in neighboring transformed cells. We will utilize DNA chips to compare the gene profiles of transformed cells cocultured with nontransformed cells to transformed cells and nontransformed cells grown alone. The hypothesis will be proven if the expression levels of some genes, but not others, in transformed cells are affected by contact with nontransformed cells during heterologous growth control.